THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

[18:00:03]

WOLF BLITZER, CNN ANCHOR: The man caught on camera only moments before the deadly subway explosion. Are there even more suspects at large?

Aimed at Americans? Growing suspicion the airport bombings were timed and located to kill the maximum number of U.S. citizens as they prepared to board flights home from Belgium. Dozens of nationalities are among the victims. Were the killers trying to single out one?

And spousal spat. As terror shockwaves spread, a new war erupts between two Republican presidential candidates, Donald Trump and Ted Cruz fighting over their wives and a series of jaw-dropping tweets. Now an outraged cruise is calling Trump a sniveling coward. How will the GOP front-runner respond?

We want to welcome our viewers in the United States and around the world. I'm Wolf Blitzer. You're in THE SITUATION ROOM.

ANNOUNCER: This is CNN breaking news.

BLITZER: Breaking news and a chilling terror revelation tonight. U.S. counterterrorism officials are telling CNN that investigators know of multiple ISIS plots in Europe in various stages of planning. They say the plots are possibly linked to the terror cells that carried out the attacks in Brussels and Paris.

Also, a senior Belgian counterterrorism official is telling CNN that investigators believe the Brussels ISIS cell was composed of two teams, one team allegedly planning a larger attack or a series of attacks, but after the arrest of the Paris terror suspect Salah Abdeslam last week, that investigators believe the second team launched the airport and subway attacks.

And the manhunt tonight expanding, with police now looking for a second suspect caught on camera at the scene of the subway bombing. He's believed to be on the run, as is the man in the light colored clothing seen with the suicide bombers at the Brussels Airport.

We're covering all angles of the breaking news this hour with our guest, including the chairman of the House Foreign Affairs Committee, Congressman Ed Royce. And our correspondents and expert analysts, they are also standing by. Let's begin with CNN justice correspondent Pamela Brown.

Pamela, major new developments tonight in the terror investigation. What are you learning?

PAMELA BROWN, CNN JUSTICE CORRESPONDENT: That's right, Wolf.

U.S. officials say a combination of electronic intercepts, human sources and database tracking indicate possible targets have been picked out by ISIS operatives over last few months. And the concern tonight is that others believed to be connected to the Brussels cell and Paris cells will launch more attacks in Europe in the near future.

(BEGIN VIDEOTAPE)

BROWN (voice-over): Tonight, as new video emerges of the bloody chaos at Brussels Airport, investigators are analyzing new evidence indicating other potential targets had been chosen. The evidence includes maps found in an apartment connected to Tuesday's attacks, according to a U.S. intelligence source.

A Belgian counterterrorism official says investigators believe the Brussels ISIS cell was composed of two teams which were planning a larger attack or series of attacks in Belgium. After police discovered Paris ringleader Salah Abdeslam's hiding place in Brussels last week, investigators believe the second team accelerated their timetable, this as investigators are now searching for a second unidentified suspect.

A man was spotted on surveillance video at the Molenbeek metro station holding a large bag just before the deadly explosion, according to Belgian state media. Investigators believe that second suspect is alive and on the run, along with this unidentified man spotted on airport surveillance video. They say he dropped off a massive bomb before fleeing.

And we're learning more about the three identified suicide bombers, 24-year-old Najim Laachraoui, the alleged Paris bomb-maker who set off one of the explosions at the Brussels Airport.

Ibrahim El Bakraoui, the other suicide bomber at the airport, he was arrested in Turkey last June and deported, and his brother Khalid who detonated the bomb at the metro station. Belgium's interior minister offered to resign today, admitting that Belgian authorities missed an opportunity to stop Ibrahim El Bakraoui after he was arrested in Turkey last June and deported.

JAN JAMBON, BELGIAN INTERIOR MINISTER (through translator): I think it is justified that people ask questions, that people ask how is it possible that someone was released early and we missed a chance when he was in Turkey to detain him?

BROWN: Belgian officials say they believe El Bakraoui's brother Khalid used a fake I.D. to rent a safe house where some of the Paris attackers hid out and where police arrested Salah Abdeslam.

(END VIDEOTAPE)

BROWN: And after police discovered Abdeslam's hiding place last week, investigators believe the second team, including suspected bomb-maker Najim Laachraoui, accelerated their timetable. They believe the second team consisted of the Bakraoui brothers and at least two others now on the run -- Wolf.

What we know so far is that these raids are ongoing, unfolding as we speak. They are taking place in the Paris suburb of Argenteuil. Now, we just heard from the French interior minister. He said that they believe they have foiled a significant plot, that it was in an advanced stage.

Essentially, earlier today, they arrested a person who was a high- level threat. That person then led to this tip which precipitated these ongoing raids. Now, the interior minister also asked journalists essentially to refrain from speculating too much, to refrain from asking too many questions, to understand that this is an ongoing, fluid and potentially dangerous situation.

But he also stressed that this was the result of a weeks-long investigation that relied heavily on European cooperation. Obviously, European leaders across the continent really trying to show the rest of the world they are cooperating, that they are sharing information.

And so, essentially, we're waiting to hear more about what the specific target of this attack was, when it was supposed to take place but what we know so far, just to recap, that this attack was in an advanced stage and that a high-level threat has been aborted, essentially, one person arrested, and those raids still ongoing, Wolf, in the Paris suburb of Argenteuil.

BLITZER: Any indication this individual arrested has a connection to the November Paris terror attacks or the more recent attacks this week in Brussels?

WARD: So far, there is no indication of that, Wolf. We simply don't know.

The only thing we do know is that he is a French national. Obviously, with the Paris and the Belgium attacks, most of the perpetrators involved were either French nationals or Belgian nationals, with the exception of two Iraqi nationals who also participated in the Paris attacks. But at this stage, we're seeing a really common thread here, which is European leaders being quite tight-lipped, trying to give as little information to journalists as they can, for the obvious reason, of course, that they don't want journalist activity to tip off people in the larger network and Potentially threaten these ongoing operations -- Wolf.

BLITZER: Which certainly makes a lot of sense.

All right, Clarissa, thank you very much, Clarissa Ward joining us from Brussels.

Let's get some more on all of this.

Joining us now, the chairman of the House Foreign Affairs Committee, Republican Congressman Ed Royce of California.

Mr. Chairman, thanks very much for joining us.

I want to get your reaction, first of all, to the news that there could be multiple terror plots in the works right now. How likely would it be for another plot to go off in Europe in the midst of all this information that's being released?

REP. ED ROYCE (R), CALIFORNIA: Very likely.

I had the conversations with European authorities. Not only is Scotland Yard overwhelmed here, or feel they are, but the continental Europeans in particular. And Belgium is a case in point where there were grave concerns about just the sheer number per capita of people coming from Belgium to train with ISIS, and then going back with the skill set.

This is the problem in Europe. The continental Europeans are overwhelmed right now in terms of their ability to keep up with the sheer numbers of former terrorists coming or terrorists who participated in training with ISIS in the Middle East and then come back to carry out these attacks.

BLITZER: Mr. Chairman, it was revealed also today by Belgian authorities that they are seeking a second suspect from that Brussels metro bombing. What, if anything, are you hearing about this person?

ROYCE: No, I haven't heard a lot about this individual.

I think the bomber, Najim, the bomber who obviously is now dead who carried out the bomb attacks in the first Paris attack, he clearly committed suicide here in this last attack.

But in terms of the ability to keep up with these individuals, here's the problem, Wolf. The strategy should be to have a comprehensive strategy and deploy it to defeat ISIS, so as to end their ability to use their training facilities to keep putting these individuals back into Europe with the order of attacking.

There's no way we're going to be able to monitor the whereabouts of these individuals and catch them after the fact. What we need to do is to go forcefully forward with a plan to defeat ISIS and remove the...

(CROSSTALK)

BLITZER: You don't see that happening by the United States right now, a specific plan to destroy ISIS?

ROYCE: No. There was a law that we put into effect giving direction to the executive branch for the president to come up with a strategy to do exactly that.

[18:10:09]

For those of us that have advocated for a long time for, you know, forward-deploying some of our special operations people, for arming the Sunni tribes and arming the Kurdish military that are doing the fighting, for changing the -- and creating a much more robust list of rules of engagement for our Air Force there, for those of us that feel that all of that is necessary in order to push ISIS into obliteration, take them out of Raqqa and out of all the other cities that they hold, we don't see this happening.

Instead, we see them expanding into Libya. We see them expanding around the globe, including in Afghanistan. And we see the same arguments about whether or not we're going to use our airpower to hit them in Afghanistan. We watched that same argument play out that we had for some 12 months before we even hit ISIS with respect to their expansion out of Raqqa in Syria.

So we need to have the United States lead on this. Leading from behind is not working for us here.

BLITZER: Your colleague the House Intelligence Committee Chairman Devin Nunes, a man you know, says it looks like Americans were actually targeted in these Brussels attacks.

Do you believe that to be the case, since the first bomb went off at a location at the airport terminal where flights to the United States were about to take off? The second bomb went off close to a Starbucks at the airport terminal, and at least a dozen Americans have been injured and on who knows how many of the 31 killed are Americans.

ROYCE: Oh, I think Devin is exactly right on that.

When the bomb is placed before the American Airlines counter, and it's just before the flight to Philadelphia, and on top of it, you combine that with what ISIS has said about targeting American targets, as well, of course, European targets, which explains the E.U. and so forth and the metro stop, but the reality is the targeting is on Americans and Europeans.

And we can expect more of it. And, unfortunately, that targeting obviously is not just confined to Europe. They will attempt -- and this is why the United States has to be ever vigilant on this. They will attempt to carry out more of those style attacks and take it into the United States.

BLITZER: Mr. Chairman, stand by for a moment. We have more information coming in. I will need you to answer some more questions.

We will take a quick break. Much more with the chairman of the House Foreign Affairs Committee right after this.

(COMMERCIAL BREAK)

[18:17:03]

BLITZER: We're following the breaking news. U.S. counterterrorism officials are telling CNN that investigators now know of multiple ISIS plots in Europe in various stages of planning.

We're back with the chairman of the House Foreign Affairs Committee, Republican Congressman Ed Royce of California.

Mr. Chairman, weeks after the Paris attacks back in November, it was discovered that someone in the Belgian terror cell was actually keeping tabs on a nuclear researcher there and could have been trying to build what's described as a dirty bomb. How can the United States stop ISIS from doing that?

ROYCE: Well, there's a couple of points here.

One, again, I would go back to the argument that we need to take the war to is. Wipe them out in Raqqa. Take away the land they hold and the training they're doing. Secondarily, I have held hearings, including down on the southern border, on this issue of possible penetration of a dirty bomb into the United States.

And in the past, we have held these hearings in order to look at how we could better beef up our border security. This is another important step that we have to take. A third step is one that we have taken, and that is in changing the law with respect to the visa waiver program, so that we don't automatically bring people in from Europe with European passports who have gone to Syria, come back to Europe, and then come into the United States with intent to do harm.

That makes it harder to introduce such a device into the United States, in the continental United States. So all of these steps need to be taken in tandem starting with that first principle, that first point. If you take away the command and control center in Raqqa for ISIS and you take away their ability to train there, you have really set back this movement.

As a matter of fact, you have taken down their capability to recruit to a large extent as well.

He says, for example, Turkey deported Ibrahim El Bakraoui, one of the terrorists, flagging him, actually flagging him to Belgian authorities. Interpol had a wanted notice out for his brother, one of the other suicide bombers.

What's going on over there? Whose fault is this? It looks like there were multiple intelligence, law enforcement failures in Belgium.

ROYCE: Well, as we discussed earlier, it's long been a concern, and this sort of confirms it in terms of the ability of the Belgian state to handle the sheer number of ISIS fighters that have come back into Belgium, first of all.

And second, those from elsewhere in Europe tend to go to Belgium in order to plan their operations because Belgium, being a small country, doesn't have the type of law enforcement capacity that, for example, the French do, nor do they have the kinds of relationships with other states, other allied states in this fight against ISIS, that allows them to effectively use intelligence quickly.

[18:20:10]

And so it's a pretty bureaucratic system over there in Brussels.

BLITZER: Yes. Obviously, as I have said, they need some sort of commission of inquiry to review the blunders that occurred and learn from them so it doesn't happen again. I would highly recommend that they do that.

Final word. Go ahead.

ROYCE: Let me share with you -- let me share with you an irony. We brought a bill by Lee Zeldin just before we -- just the day before the attack.

And the focus was on states like Belgium and setting a minimum standard for their airport security, for their methodology of trading information with us about those who fly out of those airports. And it's something that is really needed, because we have got considerable leverage and we have got a lot of expertise that we can give to the Belgians and others.

They need to accept that expertise and step up their game, because this is the consequences of -- partly, of not being prepared. You can't fully prepare, but at least you can be state-of-the-art. And the United States has done a lot of good work on this and needs to share that intelligence and they need to accept it.

BLITZER: Yes. Good point, Mr. Chairman. Thanks very much for joining us.

ROYCE: Thank you.

BLITZER: Ed Royce is the chairman of the House Foreign Affairs Committee.

There's much more breaking news coming in to THE SITUATION ROOM right now, including more details of multiple ISIS plots believed to be in the works right now in Europe.

Also, Donald Trump and Ted Cruz, they are engaged in a bitter war of words involving their wives. And Senator Cruz is livid.

(BEGIN VIDEO CLIP)

SEN. TED CRUZ (R-TX), PRESIDENTIAL CANDIDATE: I don't get angry often. But you mess with my wife, you mess with my kids, that will do it every time. Donald, you're a sniveling coward, and leave Heidi the hell alone.

(END VIDEO CLIP)

(COMMERCIAL BREAK)

[18:26:35]

ANNOUNCER: This is CNN breaking news.

BLITZER: All right, there's breaking news coming in to THE SITUATION ROOM right now.

Officials say ISIS is planning to follow the bombings in Belgium with new attacks on multiple targets throughout Europe. Meanwhile, CNN has learned that a large counterterrorism raid is under way in Brussels right now.

Our senior international correspondent, Nick Paton Walsh, is at the site of the ongoing operation.

Nick, what are you seeing? What are you hearing? What have you learned?

NICK PATON WALSH, CNN SENIOR INTERNATIONAL CORRESPONDENT: Well, Wolf, at this stage, that's relatively quiet here in the Schaerbeek area of downtown Brussels.

But right down the end of the street, you get about four or five large white trucks. The police have been moving around them. One appears to be a truck for dogs potentially sniffing out explosives or other substances there. There's quite a large number down that road, but more importantly, a very large area sealed off, this road here, but also the roads that span about four or five blocks continuing around this area.

Unclear quite why such a large amount of territory has to be sealed. We have locals here complaining. Many of them can't simply get back to their homes in the kind of light drizzle here we're seeing, and also reports that perhaps in the past hours or so people have heard helicopters in the skies above.

Clearly, there has been some intense activity here, perhaps more intense in the past hours or so, but a substantial area sealed off here. Remember, Wolf, there are two individuals at least, if not three, who police are still searching for, the man in the white seen in CCTV in the airport, another man seen in CCTV outside of the metro station.

It's unclear whether he died in the metro blast as well, and potentially two accomplices of Salah Abdeslam, Khalid and Ibrahim, may we well also be part of their investigation now, but fears that that cell may potentially have had other plans afoot, the ones which were expedited here in Brussels by the arrest of Abdeslam, of course, a key part of the explosion.

But a number of explosives, 40 pounds worth, left behind in the flat causing many to be concerned that there were other perhaps plots afoot which maybe these raids here behind me may somehow be connected to try and stop.

BLITZER: Enough bomb-making material to kill many, many more people. Nick Paton Walsh, we will check back with you.

Paul, what do investigators know about these other ISIS plots that are in the works right now linked to both Paris and the Brussels cells?

PAUL CRUICKSHANK, CNN TERRORISM ANALYST: Well, Wolf, as Pamela Brown has been reporting, there's been human intelligence, signals intelligence, intercepts coming in suggesting that there are several plots in the works from ISIS operatives in Europe at various stages of planning, that they were set in motion in the wake of the Paris attacks.

But authorities are trying to untangle exactly what the threat is. Intelligence is often more an art than a science. There's often fragmentary intelligence coming in.

But I can tell you this, Wolf. They are very, very concerned right now that ISIS is accelerating its international attack plotting in Europe. And Belgium has borne much of the brunt of this. There's a major ISIS network that has managed to establish itself in Belgium, in Brussels, that network responsible for the Paris attacks, and the Brussels attacks, the very same cell responsible for those, too.

[18:30:15] The concern now is that some of that network still at large in Brussels, still can have access to bombs and guns. And we could see another terrible day unfold soon.

BLITZER: You also have some additional details I'm told, Paul, on the structure of the cell that actually carried out the Brussels attacks. What have you learned?

CRUICKSHANK: That's right, Wolf. According to a senior Belgium counterterrorism official, they believe, investigators, that there were two teams who were going to be part of either a larger attack or string of attacks that were planned for some later date.

Well, team one was composed of Salah Abdeslam and the overall ringleader, Mohamed Belkaid, and another individual. They were holed up in a safe house in Brussels last Tuesday when Belgians security services essentially stumbled on their apartment. They weren't expecting them to be there. There was a firefight. And when they went in they discovered a Kalashnikov. They discovered

detonators, an ISIS flag, ammunition. All this suggesting Salah Abdeslam and those members of that first team were going to be part of a gun and bomb Paris-style attack on the streets of Brussels.

Then, the second team, when they got wind of the fact the safe house had been raided, that Salah Abdeslam had been arrested, they were worried, authorities believed the net was closing in on them. So they pushed the accelerator button on the plot, a smaller plot than was originally intended but a horrible, devastating attack nonetheless on the metro. They had so much explosive there, enough for a cell which is at least twice as big because there are other people, Wolf, who were involved in this network in Brussels that had already been arrested.

BLITZER: Evan, what are you learning about efforts under way to disrupt these terror plots that may be in the pipeline?

EVAN PEREZ, CNN JUSTICE REPORTER: Well, officials call it a ticking time bomb. And the frustrating thing for them is that the attackers have all the advantage. They know when they can attack. They can pick targets of opportunity, plenty of soft targets. The Belgians today lowered their terror readiness level.

Here in the United States, people feel that certainly it's still at the highest levels. They are very concerned an attack could be in the offing, but they've been seeing this. They know very little about the specifics of what could be coming and that's what's frustrating them.

BLITZER: Michael, what are these details we do know about these plans that may be in the works of ISIS. What does it say about what ISIS has in mind to do throughout Europe and, in fact, even here in the United States?

MICHAEL WEISS, CNN CONTRIBUTOR: Well, Wolf, what I've been hearing from actually inside of is and from people who have recently left is that Paris was a sea change for them. The staggering success of that operation has meant that Muhammad al Adnani's call for 2014 for foreign operations, essentially phase two of the caliphate, they are putting everything they can into this. And they've got many, many Europeans that have trained up in Syria who have been dispatched back into Europe.

The number that I've seen reported this week is something like 400. I actually believe it's much higher than that, and they are absolutely now scrambling to accelerate plots that have been under way. I've heard that Germany is a very possible likely target, in fact.

I mean, again, take this all with a pinch of salt given the providence of the source, but they are in a very boastful mood about this. They think they can absolutely paralyze Europe. And Europe is indeed, that's got the bull's-eye on it more than North America.

BLITZER: You believe, Michael, that's why the State Department issued this extraordinary travel alert this week in the aftermath of the Brussels bombings? Terrorist groups continue to plan near-term attacks throughout Europe, targeting sporting events, tourist sites, restaurant and transportation. In effect, telling Americans be very careful if you are planning on going to Europe any time soon.

WEISS: For the first time in my life, I won't travel to Europe. Let's put it that way. I'm taking it that seriously.

BLITZER: Really?

WEISS: Yes.

BLITZER: Because of imminent terror plots?

WEISS: Yes.

BLITZER: Paul, let me get your thoughts on that. You are from Belgium. You were born there. You know that country and all of Europe right now.

Paul, what do you think?

CRUICKSHANK: Well, people are scared, Wolf. There's no doubt about it.

I mean, ISIS have succeeded in really scaring the European publics because there really is a significant threat. The arithmetic is really worrying more than 6,000 European extremists who have traveled to Syria and Iraq. Many of them joining ISIS, 1,500 who have come back and this is beyond the capacity European security services to keep Europe safe right now, to prevent these attacks getting through.

And a lot of these jihadists that have joined ISIS have pre-existing ties to criminal networks, petty crime.

[18:35:01] That means they can easily get hold of automatic weapons, Kalashnikovs and deadly as we saw play out in Paris. I mean, just with a few Kalashnikovs, you can create absolute carnage. I think the U.K., there's slightly less of a threat there because there's fewer guns in the U.K. that are available on the black market. You need to smuggle them in.

I think the countries most at threat right now, Germany, I agree with. Holland is also under threat, because it's part of that anti-ISIS coalition. And, Wolf, before the Paris attacks, there was fragmentary intelligence that came in to Western intelligence that ISIS was planning an ambitious plan to attack five European cities, including Paris, a major city in Belgium, but also Berlin and London and another city.

Well, they've hit two of those five so far. Cities in Germany, cities in the Netherlands, I think, especially vulnerable moving forward. ISIS will want to send a statement they can hit all these countries. What they want to provoke, Wolf, is a backlash against Muslims in Europe because they think that's going to help them with their recruitment. The way things are going right now, there's real worry about social cohesion across the European Union.

BLITZER: We have to take a quick break.

Just want to remind our viewers, this travel advisory from the State Department was not just for Belgium. It was in their words throughout Europe. U.S. citizens should exercise vigilance when in public places or using mass transportation. Be aware of immediate surroundings. Avoid crowded places. Exercise particular caution during religious holidays and at large festivals or events.

Much more on the breaking news right after this.

(COMMERCIAL BREAK)

[18:41:25] BLITZER: We're watching multiple anti-terror raids under way right now -- one in Brussels, another near Paris. These come amid concerns the Brussels terrorists were targeting Americans when they set off bombs at the Brussels airport.

We're back with our terrorism analyst.

Paul, authorities are searching right now for what they say is a second suspect in that metro attack who may have escaped. We know one airport bomber escaped as well. Salah Abdeslam escaped after Paris. What role does this escapee, shall we call him, play in the attacks right now?

CRUICKSHANK: Well, they are trying to figure that's out, Wolf, at this hour. With the metro attack, it appears that this individual was on the platform with one of the Bakraoui brothers, who was the metro bomber, and one of the Bakraoui brothers went into the metro carriage and then you have, of course, the explosion as the train is pulling away from the station, as I understand.

And on the CCTV footage, this individual is pictured at the metro station with a large bag. Of course, we know that this cell has used suitcases to put bombs inside. So, one of the worries is, what's is in that large bag? Where did he go? And who might he be linking up with next?

Might one of those people be that third individual seen at the airport, the individual seen with a cap and a light anorak who for whatever combination of reasons abandoned his suitcase bomb and started running from the scene. Did he decide to back out of the plan? Did something not work? What is he going to do next?

What we have seen, Wolf, with this cell and it's the very same cell behind the Paris attack is a lot of determination to carry through with attacks. If at first they don't succeed to try again until they can go to paradise from that point of view.

One last thought here, with the Paris attacks, there was that second wave plan that the ringleader in Paris Abdelhamid Abaaoud was trying to hit, a shopping center, also police commissariat, when the entire international media had descended on Paris. So, there's concern that whatever is left of this cell could launch some kind of attack with the world's attention squarely on Brussels.

BLITZER: Michael, do the Brussels targets, the new targets discovered by investigators indicate that Americans may be specifically targeted?

WEISS: Sure. I mean, the airport was targeted because they wanted to hit as many foreign nationals. And they did. And they injured, what, a dozen American travelers, including I think an air force lieutenant colonel.

Absolutely. If they can't strike us on the U.S. homeland, they're going to strike us while we travel abroad. And this is I think one of the reasons the State Department issued this travel advisory warning. Americans are the top prize to ISIS, because we are the world's superpower and, according to their conspiratorial world view, the force of all evil against Sunni Muslims in the region.

So, absolutely, they are trying to get us.

BLITZER: Evan, we know at least a dozen Americans were injured in the terror attacks in Brussels out of 300 or so who were injured. Of the 31 who were killed, they haven't officially released identities, we know there are several Americans who are listed as missing but they haven't been identified yet. None of them have been identified yet.

What are you hearing?

PEREZ: There's certainly a growing fear among U.S. authorities, Wolf, that because there's so many Americans who have not been heard from, their family members who are talking to members of their families, phones get cut off and they haven't heard from them since, they are fearing the worst.

[18:45:16] So, we may yet hear that there may be fatalities among the Americans. We don't know yet. It's not been confirmed. But it is something that is -- that's one reason why we have the FBI there in Brussels trying to assist the Belgian authorities because it is something at the top of their agenda.

BLITZER: All right. Guys, stand by.

As the hours pass since the attacks, families of the missing, some of them American, are facing the very grim possible that their loved ones will never come home. Sasha and Alexander Pinczowski were on their phone with their mother while checking in for their flight back to the United States when the call went dead. Emily Eisenman was looking forward to seeing her boyfriend Bart Migom who was about to fly from Brussels to Georgia for a visit. She called to check on him but no one answered.

(BEGIN VIDEO CLIP)

EMILY EISENMAN, BOYFRIEND MISSING IN BRUSSELS: In the last two days, they have been something I never thought I would feel. It's been the worst days of my life. I guess I didn't know how much one person can love another until you just don't know where they're at.

(END VIDEO CLIP)

BLITZER: Andre Adam was waiting for a flight to Miami with his wife Danielle when the explosion tore through the terminal. Danielle was found injured, but alive. Andre is still missing.

And then there's missing couple from Tennessee, Stephanie and Justin Shults who are at the airport during the attack. Family members say the State Department told them the two Americans were injured but a Belgian official later contacted Justin's mother and said that information was incorrect. Justin's brother says he'll keep praying for the couple to be found alive and well.

We'll be right back.

(COMMERCIAL BREAK)

[18:51:22] BLITZER: We're covering the breaking news. Belgium authorities just announced arrests in new raids across Brussels.

Let's go to our terrorism analyst Paul Cruickshank.

What else are you learning, Paul?

CRUICKSHANK: Wolf, the Belgium interior minister Jam Jambon has just tweeted that there's been a major counterterrorism operation in Schaerbeek in Brussels. We've been seeing some of that play out as Nick Paton Walsh has just been reporting. But he has announced five arrests.

This appears potentially to be a significant breakthrough. Quite how it relates to the Brussels attacks we await to hear, but the tenor of this tweet suggests a significant breakthrough tonight -- five arrests. They may be major arrests.

BLITZER: Paul Cruickshank, thank you. We'll stay on top of this story and get back to it.

But we're also following important developments in the campaign for the White House, including the highly personal skirmish that's quickly escalating between Donald Trump and Ted Cruz.

Our political reporter Sara Murray is following the presidential race. She's here in THE SITUATION ROOM.

This is pretty dramatic stuff. What's going on?

SARA MURRAY, CNN POLITICAL REPORTER: That's right, Wolf. Politics has taken a turn for the ugly today. Donald Trump is going after Ted Cruz's wife. And we saw a very angry response from Ted Cruz on the trail today, as he argues that family members should be off-limit off- limits.

(BEGIN VIDEOTAPE)

SEN. TED CRUZ (R-TX), PRESIDENTIAL CANDIDATE: It's not easy to tick me off. I don't get angry often. But you mess with my wife, you mess with my kids, that'll do it every time. Donald, you're a sniveling coward, and leave Heidi the hell alone.

MURRAY (voice-over): For Ted Cruz, the 2016 campaign attacks just got a little too personal. That's after Donald Trump retweeted a split screen image of Cruz's wife Heidi and his wife Melania, with the caption, "The images are worth a thousand words."

Trump's insult comes after he threatened to spill the beans about Cruz's wife after an old modeling photo of Melania Trump posing nude appeared in a Facebook ad, even though the ad came from a anti-Trump super PAC and not the Cruz campaign.

CRUZ: Donald does seem to have an issue with women. Donald doesn't like strong women. Strong women scare Donald.

Now, Donald is scared a lot these days. Donald is scared to debate. He ran away from the last debate that was scheduled because he was scared of Megyn Kelly and because he was scared to defend his policies.

MURRAY: As Cruz warns a Trump nomination could cost the GOP the election.

CRUZ: Donald Trump is a train wreck and he hands the election to Hillary Clinton.

MURRAY: A new CNN/ORC poll shows Trump faces steep odds in the general: 56 percent of voters predicted Hillary Clinton could beat him in a head-to-head battle, compared to 42 percent who put Trump on top.

While the two are nearly even on who would be the strongest leader, Clinton trounces Trump on her ability to relate to middle-class problems and handle the responsibilities of commander-in-chief.

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: Thank you.

MURRAY: A strength Clinton is aiming to highlight in the wake of the terror attacks in Brussels.

CLINTON: Cannot allow our nation to be pitting groups of people against one another.

[18:55:03] And it plays into the hands of terrorists who want nothing more than to intimidate and terrorize people.

(END VIDEOTAPE)

MURRAY: Now, Donald Trump isn't one to apologize and today is no different. He took to Twitter this afternoon to say, "I didn't start the fight with lying Ted Cruz over the 'GQ' cover pic of Melania. He did. He knew the super PAC did. Hence, lying Ted" -- Wolf.

Gloria, Barbara Boxer, the Democratic senator from California, tweeted this. "Real Donald Trump has once again insulted all women. He does not deserve even one woman's vote."

How much potentially could this hurt, this latest exchange with Ted Cruz hurt him getting female support?

GLORIA BORGER, CNN CHIEF POLITICAL ANALYST: Look, he is of all the Republican candidates doing the best with Republican women, Wolf. He is up nine points over Cruz. He is almost triple over John Kasich with Republican women.

Should he become the nominee in a general election, 74 percent of women have an unfavorable view of Donald Trump. Hillary Clinton, while she has her own problems, when you pit her against Trump, she's up with women 21 points. However, he does very well with white men, and if he can make up the gender gap that way, this wouldn't hurt him that much at all.

What we see today is the fact that Ted Cruz is trying to make up some ground. Yes, he's obviously upset about what Trump tweeted about his wife, but he's kind of laid down the gauntlet today. He now has to beat Donald Trump. This is war. They're going to go to war in the state of Wisconsin pretty soon, and he's got to beat him there. And this is one way he clearly believes he can do it.

BLITZER: The next big contest in Wisconsin, April 5th.

BORGER: Yes.

BLITZER: Ron, how is Ted Cruz handling this?

RON BROWNSTEIN, CNN SENIOR POLITICAL ANALYST: I think he's handling it very well, as effectively as you can. I think, though, it's probably going to do more to hurt Trump than to help Cruz. In that sense, I suppose, it helps Cruz.

There has been a gender gap in the Republican race. Donald Trump has run consistently better among men than women. And that might benefit Cruz. And certainly, this is an extraordinary exchange that's likely to deepen those problems for Donald Trump.

The problem for Ted Cruz, though, is that the calendar is moving toward the states with fewer evangelical voters. And we've talked about before, there is no state yet in which he has carried most evangelical voters. It was I thought kind of an ominous shot across the bow today where a poll came out in Pennsylvania where he was only 11 percent among voters who are not evangelicals. The kind of problem that would make it very difficult to compete in the Northeast and leave a lane open for John Kasich to remain in this race.

BLITZER: For months, Sara, you've been out there on the campaign trail with Donald Trump. This issue of women keeps coming up. You've noticed it obviously.

MURRAY: Well, that's right. It came up with Megyn Kelly. You know, the anti-Trump super PAC ran an ad about all of the comments, he's made about women.

BLITZER: Carly Fiorina.

MURRAY: In the past, of course, there was Carly Fiorina. The interesting is, Republicans have really been loathed to bring this up. They feel it is more like an attack Democrats would make.

But Democrats are sitting by chomping at the bit to make this an attack. You can bet that everyone who is supporting Hillary Clinton is already building a file of these comments Donald Trump has made about women and they're going to use them against him in the general election. It just took him actually attacking a Republican's wife for this to really come up.

BORGER: And, you know, given what's going on in the world right now, Hillary Clinton gave a foreign policy speech yesterday, which was political and was clearly aimed at Donald Trump, but a serious speech. And here you have in the middle of Brussels, you have Ted Cruz and Donald Trump fighting over pictures of their wives.

And I think it's unseemly. I think if you're an independent voter out there and you're thinking down the road about the general election, this is clearly something that's going to come up about the level of debate in the Republican Party.

BLITZER: Ron, go ahead.

BROWNSTEIN: Well, you're looking at in Donald Trump a candidate with unprecedented, unfavorable ratings among the general public to be in this position. I mean, Hillary Clinton is in a weak position too, but if you look at the new CNN/ORC poll, he's looking at an unfavorable rating among the key groups in the Democratic coalition, 82 percent among non-white voters, 77 percent among college educated whites.

As Gloria said, almost 75 percent among women. We don't have millennials in this new poll breakup. But in other polling, it's been also around 75 percent.

Now, Hillary Clinton is weak too in the core Republican groups, but her showing is not as bad as Donald Trump is among those Democratic groups. And so, what you have this situation where Republicans are kind of looking at Trump, growing more and more uneasy about his ability to contest a general election, trailing eight straight national polls published this month, trailing Hillary Clinton. And yet, unable to coalesce behind one alternative, allowing him to motor toward the nomination as a plurality frontrunner.